1. Field of the Invention
The present invention relates to an engine control method for controlling fuel injection and ignition of a 4-cycle multi-cylinder internal combustion engine. More particularly, the present invention relates to an engine control method for a multi-cylinder engine, which is based on sensed engine intake pressure, and which is configured to shorten a period from a start of cranking until the fuel injection control is enabled.
2. Description of the Background Art
There is known engine control apparatus having a manifold pressure sensor (a Pb sensor or an intake air pressure sensor) for measuring an engine intake pressure. The engine control apparatus is configured to recognize a pattern of an intake air pressure waveform (a Pb waveform) obtained from engine intake pressure data detected by the Pb sensor, and to carry out a stroke determination for respective cylinders during a starting operation of the engine.
In Japanese published Patent Document JP-A-2007-56732, a fuel injection control apparatus is disclosed, which settles a stroke determination based on a Pb waveform, after approximately three cycles (1 cycle corresponds to 720 degrees of crankshaft rotation) subsequent to starting cranking of the engine. The fuel injection control apparatus of Japanese published Patent Document JP-A-2007-56732 is configured to carry out a group injection, such that fuel is injected simultaneously to synchronous cylinders until the stroke determination is settled. Subsequently, a sequential injection for each cylinder is started.
In a four-cycle engine having four cylinders, a first cylinder group including first and fourth cylinders is operated synchronously, and a second cylinder group including second and third cylinders is operated synchronously, in terms of mechanics and at reverse timing in terms of stroke. For example, when the first cylinder is at a compression top dead center position, the fourth cylinder is at an exhaust top dead center position. Therefore, in the group injection as described above, cylinders which are suitably injected in the intake stroke are two from among all the four cylinders.
However, when influences on exhaust gas or the like are considered, it is preferable to adjust the amount of injection to these two cylinders further to an adequate amount. In order to adjust the amount of injection in the group injection to an adequate amount, it is desirable to control the amount of injection based on the intake air pressure detected by the Pb sensor. An adequate detected value of an intake pressure can easily be obtained from the Pb sensor, even when the throttle opening is low.
Also, since a correspondence between the intake air pressure value detected by the Pb sensor and the crank position in one cycle (720 degrees) is not known until the stroke determination is settled, the value detected by the Pb sensor cannot be immediately used for controlling fuel during starting operation of the engine.
In the disclosure of the Japanese published Patent Document JP-A-2007-56732, approximately three cycles are required from the start of cranking until the stroke determination is settled, and therefore, a period until the fuel injection control is enabled for individual cylinders, based on an intake pressure detected by the Pb sensor, is long. Also, when using a method of starting a calculation of data required for fuel injection control based on the value detected by the Pb sensor after having settled the stroke determination, the period is further elongated.
Although the known engine control methods have some utility for their intended purposes, a need still exists in the art for an improved engine control method. In particular, there is a need for an engine control method which overcomes the difficulties encountered with the known art. Accordingly, it is one of the objects of the present invention to provide an engine control method which solves the problems encountered in the related art, and which, based on sensed engine intake pressure, is configured to shorten the period from the start of cranking until fuel sequential injection control is enabled for individual cylinders.